Conventionally, the power boilers of the invention are provided with so-called water tube walls, which consist of adjacent water tubes with plate-like fins therebetween. The purpose of the water circulating in the water tubes is to recover heat generated in the combustion. However, such a water tube wall is, considering its size, relatively light in structure and does not endure additional stresses as such without bending. These stresses can result, for example, from variations in the flue gas pressures, and, thus, the wall must be supported to maintain the desired shape. Furthermore, it is known that when the water tube wall is provided with additional equipment, the thermal expansion in the walls and in the whole boiler must be taken into consideration.
The panel-structured walls of the previously described type are conventionally stiffened by utilizing horizontally extending buckstay systems, or frames comprising beams connected to one another through corner link assemblies, in a manner allowing relatively free differential thermal expansion between the hot furnace walls and the cooler beams. The number of the beam frames is determined by the stiffness of the furnace walls, which, again, is affected by the size and distribution of the tubes in the water tube wall. The beams forming the frame are dimensioned as simply-supported beams, whereby their size is determined based on the width of the wall and the vertical distribution of the beams.
Supporting arrangements of power boiler walls according to the prior art are disclosed, for example, in patent specifications and published applications U.S. Pat. No. 3,379,177, U.S. Pat. No. 3,814,063, U.S. Pat. No. 3,368,535, European Patent No. B1-0 591 183, Japanese Laid-Open Patent Application No. A2-2001-304505, No. A2-2002-257303, No. A2-2000-2401, No. A2-06-193809, No. A2-52-113401, No. A2-8-296807, and No. A2-11-241805.
U.S. Pat. No. 3,379,177 discloses a power boiler and the supporting structure of its walls. The publication discloses one known manner of constructing a power boiler. A substantial part thereof is that the whole boiler structure is suspended to hang on steel structures, more specifically, to hang on a supporting plane belonging to the steel structures and being located above the boiler in such a way that the supporting structures of the boiler walls are also suspended to hang on the supporting plane. The supporting structures of the walls comprise vertically spaced buckstays located perpendicular to the water tubes against each outer wall of the boiler. The attachment of the buckstays allows some movement between the wall and the buckstay to allow for the thermal expansion/contraction of the wall in the direction of the buckstay. The buckstays, on the other hang, are slidingly supported against vertical I-beams of their side opposite to the wall of the boiler. There are several I-beams across the width of each wall and they are suspended, as already mentioned above, to hang on the steel structures of the boiler building, i.e., to hang on the above-mentioned supporting plane. These vertical I-beams, in turn, are supported by a horizontally positioned beam frame welded to the I-beams of the side opposite to the buckstays and comprise rigid beam trusses located on each side of the boiler. These beam trusses form the beam frame surrounding the boiler by means of flexible corner link assemblies, which, for their part, allow for the changes in the outer dimensions of the boiler, which result from the changes in the temperature.
U.S. Pat. No. 3,814,063 also discloses a top-supported power boiler and, more accurately, an alternative way of carrying out a support structure of a water tube wall. In this arrangement, the water tube wall is connected to I-beams, which are attached, in the same way as the boiler, from their top, to hang on a supporting plane, but spaced apart from the boiler, by means of rods joined at both ends, so that one end of the rod can side with respect to the vertical beam. The joined rod is connected to the water tube wall by means of a substantially square leg portion extending across a number of water tubes. The vertical I-beams, again, are attached to a horizontally positioned truss structure, surrounding the whole boiler, form the sides opposite to the joined rods.
Japanese Laid-Open Patent Application No. A2-2001-304505 also discloses a top-supported power boiler hanging from a support plane of the upper part and an apparatus, by means of which vibration and swinging motions of the power boiler are prevented, for example, during an earthquake. At the same time, a support arrangement for the walls of a power boiler is disclosed. In the discussion of prior art in the publication, there is disclosed a method of attaching the buckstays substantially horizontally to a wall of the power boiler, in such a way that the attachment thereof allows for differential thermal expansion of the wall and the buckstay. The buckstay is actually attached to the wall by means of a specific mounting eye in such a way that the mounting eye is attached to the boiler wall. The buckstay is attached to the mounting eye by a bolt, for which, however, there is arranged an oblong hole to the buckstay, which allows for the differential thermal expansion of the boiler wall and the buckstay by allowing sliding in the longitudinal direction of the attachment bolt in the hole. The buckstays have been attached to vertical rods from the sides opposite to the boiler in the groups of a few buckstays, in such a way that one buckstay from each group is stationarily attached to the rod, while the other buckstays are allowed to slide in the longitudinal direction of the rod in a manner required by the thermal expansion of the boiler wall. The rods, in turn, are attached to steel structures of the power boiler supported to the ground in a manner allowing vertical sliding. In other words, they are attached in such a way that the thermal expansion of the boiler walls does not direct any vertical forces to the steel structures. In other words, both the buckstays and the vertical rods attached thereto are suspended by means of the boiler to hang on the supporting plane of the upper part of the steel structures of the power plant.
Among other things, it is a typical feature of all arrangements disclosed in more detail above, as well as of all other arrangements mentioned in the above-mentioned publications, that the supporting structures of the boiler walls are suspended to hang on the supporting plane of the upper part of the steel structures of the boiler building, either together with the boiler or by means of special separate suspending means.
Such a suspending of support structures, however, brings about some disadvantages. Whether the suspending has been done by either of the above-described manners, the weight of the supporting structures, which consist, depending on the method of suspension, at least of the buckstays, the vertical beams connected to the buckstays and the possible truss structures connected to the vertical beams, forms a considerable part of the total load to the steel structures. Furthermore, when the size of the boilers increases, it is evident that the weight of the supporting structures increases at least in the same ratio. Thereby, naturally, the steel structures used for suspension of the supporting arrangements of the boiler and the walls thereof must be increased in the same ratio with the increasing loadings.
It is, however, possible to minimize the problems by changing the support of the water tube walls, such that the majority of the support comes directly from the foundations, or the like, without any top-supported suspensions of the prior art. Furthermore, the weight of the supporting structures loading the upper supporting level of the boiler can be reduced by modifying the supporting structures of the boiler walls in such a way that the system works by lighter buckstays or even by arranging as large a portion of the supporting structures as possible to be ground-supported or supported to the foundation of the boiler building without a need to suspend the supporting structures to hang on the supporting plane of the upper part of the boiler.
Another problem encountered is that the buckstays are subjected to considerable stresses, regardless of the manner in accordance with the prior art, by means of which, they are arranged into connection with the boiler walls. This is because the buckstays are used not only for their actual purpose. In other words, the buckstays not only may be used for supporting the boiler walls against normal loads, but also, for transferring the loads against the boiler walls forward. In such structures, the buckstays are subjected at a time to at least one of compression, bending and torsion.
The above-mentioned drawbacks are solved, in accordance with the present invention, by means of a method of supporting walls of a thermal power boiler. In this method, the furnace of the thermal power boiler is suspended to hang on a supporting plane of the upper portion of steel structures especially arranged for the purpose and the walls, being formed of water tubes, are supported horizontally, at least by means of buckstays positioned substantially perpendicular to the water tubes, and vertical pillars located outside the buckstays, which pillars are attached to the ground or the foundations of the boiler building. A characteristic feature of the method in accordance with the invention is that at least two of the walls, located on the opposite sides of the boiler, are supported in such a way that loads directed perpendicularly to the walls are transferred, by means of the vertical pillars, to internal stresses of at least one rigid plane surrounding the boiler.
Correspondingly, for an apparatus in accordance with the invention for supporting walls of a thermal power boiler, the boiler comprises a furnace having walls formed of vertical water tubes and being suspended to hang on a supporting plane of the upper portion of steel structures especially arranged for the purpose, buckstays arranged outside the walls and substantially perpendicular to the water tubes for supporting the walls and pillars arranged on the sides of the boiler outside the buckstays and being attached to the ground or the foundations of the boiler building. It is a characterizing feature that at least one rigid plane surrounding the boiler is attached to the pillars and at least two of the walls, located on the opposite sides of the boiler, are supported to the pillars.
Other characteristic features of the method of and apparatus for supporting walls of the power boilers become apparent in the accompanying claims.